PK can confirm this for us but I think the DW is installed under the stove top. If that's the case, my guess is that an RV dealer or service center can order one and install it there for you. If you already have an oven there, it would have to go. If you have a slide-in cooktop/oven combo, it would have to be replaced with a cooktop only unit.
In my rig, I have and use the oven. But I'd love to put in a DW for my DW! But she'd prefer to do the dishes by hand. If she ever relented, I'd rework the island cabinet and install it there so I wouldn't have to give up the oven.
Here's a
link to the website of the manufacturer (Fisher & Paykel) of the DW that used to be offered. Not sure exactly what model was used (PK?) but you can get a sense of what's available and the specs/sizes etc.
Jim
PS: Just looked again at these units and they are really neat. Here's a link to the installation manual. Single Wash Drawer units require a rough opening of 23-5/8" wide X 16-7/32" high X 22-7/8" deep. Looks like they require a cabinet sidewall thickness of at least 5/8". This means that 1/2" or thicker plywood would have to be applied to the current thin board that is used inside the trailer cabinets.